Really, if you want any sort of ownership over your photos, you have to watermark. Even major companies are having concerns over image theft. My DH is a photographer and works for a national photography company and they have constant debates over using the Internet for marketing while protecting their images from being stolen. One of DH's current projects is designing their watermark. Unfortunately, you kind of have to make them as obnoxious as possible, otherwise they aren't effective.
I'm sorry your images were stolen. It really just sucks to put your hard work out there and have someone claim it as their own.